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    一、通过构造函数创建对象实例，
    该对象实例能够计算圆的周长和面积，固定属性是圆的半径，格式如下：
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<script>
     function circle(r){
        this.r=r
        this.mj=()=>{
            return Math.PI*this.r*this.r
        }
        this.zc=()=>{
            return 2*Math.PI*this.r
        };
     }

     let c=new circle(1)
     console.log(c.mj());
     console.log(c.zc());


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